Professional quality animal nail clippers used by both veterinarians and animal owners in trimming the nails of animals, such as those of dogs and cats, have been successfully made and sold for over forty years under the trademark "RESCO" by Tecla Company, Incorporated of Walled Lake, Mich. Such clippers were initially made in accordance with the principles and features of the Laing U.S. Pat. No. 2,955,354 and later pursuant to the improvements of the Clark U.S. Pat. No. 3,838,507, both incorporated herein by reference. More recently a nail clipper of this type has been successfully modified for use in clipping human artificial fingernails by employing the principles and features of the Reiswig U.S. Pat. No. 4,856,190, also incorporated herein by reference. Other prior art patents of general interest directed to guillotine-type cutters and clippers are disclosed in the following U.S. patents:
______________________________________ 165,402 Bates 07-13-75 205,088 Hollman 06-18-78 1,347,651 Nauth 07-27-20 1,927,234 Hawkins 09-19-33 2,820,292 Bouten et al 01-21-58 2,955,354 Laing 10-11-60 3,101,535 Andis 08-27-63 3,299,505 Pionek 01-24-67 3,430,340 Perles 03-04-69 3,838,507 Clark 10-01-74 3,845,553 Fields 11-05-74 3,855,699 Charlett 12-24-74 3,903,596 Crosby 09-09-75 4,228,585 Nelson 10-21-80 4,449,297 Fuchs et al 05-22-84 4,856,190 Reiswig 08-15-89 5,065,513 Reiswig 11-19-91 5,101,563 d'Orgelys 04-07-92 5,123,430 Davidovitz 06-23-92 ______________________________________
In general, the nail clippers made pursuant to the aforementioned Clark '507 patent comprise a guillotine-type cutter with two blades. One blade is a movable cutting blade reciprocated in a single cutting stroke by manually squeezing together the handles of the clipper against the force of a biasing spring coupled between the handles. The second blade serves as the nail retainer blade and thus has an oblong, circular or other specially shaped opening to closely receive therethrough the nail to be cut, and is attached to the larger of the two handles with one or two screws or rivets. A blade actuating link (part 32 of the Clark '507 patent and part 44 of the Reiswig '190 patent) is operatively coupled between the clipper handles and the cutting blade so that when the user squeezes the two handles together, the link pushes the cutting blade forward on its cutting stroke so that it meshes with and travels by the retainer blade. The object to be cut (e.g., animal nail) is held in the retainer blade opening so that closing the clipper handles drives the cutting edge of the cutting blade through the object to sever it. The user then releases the clipper handles, allowing the spring to pull the link which in turn pulls the cutting blade back as the handles return to their fully opened position, ready for the next cutting stroke.
Based upon the aforementioned long commercial experience, it has been found that, for the nail cutting action to work properly, some of the essential operational features are: (1) the cutting blade has to have a sharp cutting edge; (2) the cutting blade has to slidably mesh tightly with the retainer blade during the entire cutting stroke; and (3) the cutting blade should travel for a substantial distance beyond the retainer blade opening to insure that the object is severed cleanly.
Typically the cutting blade is a flat part made from hardened tool steel or stainless steel in a progressive die stamping operation. The cutting blade is ground flat on one side and a cutting edge is ground the opposite-side, and has holes or slotted openings to releasably retain or accept the link adjacent its rearward end. The retainer blade is made of like material in a progressive die stamping operation likewise ground flat. Preferably, certain slight curvatures are imparted to the cutting blade and retaining blade surfaces, as described in conjunction with the embodiment of FIG. 7 of the Clark '507 patent, to insure that the under surface of the cutting blade adjacent its cutting edge is forced closely against the upper surface of the nail holder as it slides therealong in the cutting stroke.
The large handle of the clipper typically is a stamped metal or plastic molded part to which the retainer blade is attached by one or two screws. The large handle carries a pivot pin pivotably supporting the small handle thereon.
The blade actuating link is a thin, flat progressive die stamped part that is pivotably attached near one end to the small handle, typically with a rivet. The link has a small hole adjacent the pivot pin connection to which one end of a extension coil spring is attached, the other end of the coil spring being hooked to the inside of the large handle to thereby yieldably pull the handles apart or to their fully opened positions. The forward end of the link has a notch forming a projection hook which extends through a hole in the cutting blade located near its rear edge. The material in the blade between the link hole and rear edge-of the blade forms a transverse bar extending across the link notch which the link alternately pushes and pulls on in the cutting and retraction strokes of the clipper. Although this crossed hook and bar means forms an easily releasable connection between the link and cutting blade, the link must also remain operable to alternatively push and pull the cutting blade during the blade cutting and retraction strokes respectively and therefore must stay engaged with the blade throughout these strokes and during stroke reversal.
One of the unique features of this type of linkage, as set forth more fully in the aforementioned Clark '507 patent, is that it is possible to remove the cutting blade without taking the assembly apart. The cutting blade is provided with an extra hole near its forward end for receiving a holding pin to temporarily hold the blade fixed in its extended position. The link has a tab protruding rearwardly beyond its handle pivot mounting which can be finger depressed to disengage the forward end of the link from the cutting blade and then be loosely abutted against the rear edge of the cutting blade. The retaining pin is then removed to thereby eject the cutting blade and the handles are then squeezed for easy removal from the clipper. The replacement blade can then be readily installed by reversing this procedure.
Although the aforementioned "RESCO" nail clipper has long been commercially successful and accepted as "the standard of the industry" in the veterinary profession for animal nail trimming, nevertheless certain long standing problems have remained in its manufacture and use, centering around the construction of the link 32 of the Clark '507 patent and the corresponding link 44 of the Reiswig '197 patent. These links have a contour with a rectangular notch or recess near the forward end, i.e., notch 36 of the '507 patent link 32 defined by a pushing surface 42, a bottom bearing surface 44 and a pulling surface 46 which engage the portion of the cutting blade 26 between the cutting blade hole 40 and the rear edge 69 of the blade, and similarly notch 48 of link 44 of the '190 patent. This hook configuration works adequately during the forward or cutting stroke. However, on occasion link 32 inadvertently can be pulled out of the cutting blade 26 on the retract or opening stroke, if the cutting blade becomes bound or otherwise restricted during this stroke. Also, if the nail trimmer is inadvertently dropped by the user, the link will sometimes disengage itself from the cutting blade, thereby creating a nuisance for the user and a possibly serious interference during some nail trimming circumstances.
In one proposal to solve this unwanted unhooking problem, it was suggested that the front wall 46 of the notch was to be ground after stamping to provide an acute angle or undercut to create a camming effect so that the link would more readily stay removably engaged in the cutting blade. However this would be a very labor intensive operation which would add considerable manufacturing expense to the clipper. Although this undercut angle alternatively could be imparted in the progressive die operation, thereby eliminating a grinding operation, this would cause die wear and breakage problems. Also, whether undercut or not, the rectangular configuration of the notch at the front of the link has caused added expense in the manufacture of the precision punch dies and made them prone to breakage, and also made the part as punched susceptible to burrs. Likewise, the outer perimeter of the die punch in the vicinity of the notch has areas with straight intersections at the corner that make the punch die susceptible to undue wear and breakage problems.
Another problem experienced with the link 32 of the Clark '507 patent arises from the provision of a small diameter hole 56, which receives the end hook 55 of the tension coil spring 30, and another small diameter hole which receives the pivot pin 34 for pivotally coupling link 32 to the small handle 12. These two small diameter holes require delicate punches to form the same, leading to manufacturing problems of punch breakage and/or formation of burred holes.
Another problem encountered with these small diameter link holes is "slug return". Slug return occurs when the slug of metal punched out by the punch from the sheet metal strip blank clings to the punch on the downstroke (piercing stroke) and then remains on the punch during retraction above the die section, instead of being stripped and ejected below the blank as intended. This in turn can, and often does, cause the strip stock being stepwise fed through the progressive die press to jam up, thereby requiring the press to be stopped and the die cleared before production can resume. Slug return thus represents an expensive problem whenever it is encountered in production.